Bidirectional tandem catalysis coupled with interface engineering and Se vacancies for accelerating the polysulfide conversion

The shuttling of long-chain LiPSs (Li2Sn, 4 ≤ n ≤ 8) and the sluggish conversion from Li2S4 to Li2S represent two primary challenges hindering the fast multi-step transformations of lithium-sulfur (Li-S) batteries. Here, we propose a bidirectional tandem catalytic strategy to promote polysulfide conversions. A novel nanostructured catalyst consisting of hollow bimetallic selenide (ZnSe/SnSe2) cubes with dual-active centers, heterogeneous interfaces and selenium-rich vacancies was synthesized. Experimental and theoretical calculations confirmed that ZnSe and SnSe2 selectively reduced the thermodynamic transition energy barrier of S8→Li2S4 and Li2S4→Li2S to achieve baton-relay-like conversion of polysulfides. Moreover, the synergistic effect of ZnSe and SnSe2 significantly reduced the activation barrier of Li2S reoxidation during the charging process, and achieved an efficient bidirectional catalytic conversion. In situ Raman analysis confirmed that ZnSe/SnSe2 effectively inhibited the shuttle effect. As a result, a battery with ZnSe/SnSe2 interlayer delivered high specific capacity of 1269.5 mAh g-1 at 0.2 C, and excellent rate capability (680.4 mAh g-1 at 4 C). Remarkably, the battery maintained cycling stability with only 0.086% capacity degradation per cycle after 500 cycles at 2 C. This work provides a new path for designing electrocatalyst towards precise control of catalytic processes in Li-S batteries.